1. Jim Monnich
Engineering Manager
Selecting Electromechanical Drive
Trains for Lab Instruments

2. Electromechanical: Balancing the Tradeoffs
Repeatability
Accuracy
Cost
Efficiency
Duty Cycle
Speed
Resolution

3. So where do we start with selection…

4. Think about your PET!
Precision
Expected Life
Throughput
Special

5. Resolution
Repeatability
Accuracy
Velocity
Control
Precision

6. Mechanical
Efficiency
Mechanical
Wear
Resistance
Contamination
Resistance
Maintenance
Expected Life

7. Speed
Capacity
Maximum
Acceleration
Frequency
Response
Duty Cycle
Throughput

8. Force Density
Material Cost
Implementation
Cost
Travel Length
Special
Considerations

9. Ball Screw
• Threaded rod
and matched ball
nut with
recirculating
bearings in the
screw. The
bearings
improve
efficiency and
increase duty
cycle.
Lead Screw
• Simple threaded
rod and
machined nut
with sliding
interface. In
some cases the
nut is preloaded
against the
screw to reduce
backlash.
Timing Belt
• Timing belt
attached to a
carriage with
cogged pulley.
Most simple kind
of motion.
Rack & Pinion
• Machined gear
that moves a
linear rack back
and forth or the
gear moves as
the rack is
stationary.
Linear Motor
• A row of
magnets
interfaces with
an
electromagnetic
carriage to move
a load in a linear
direction.
5 Common Linear Drive Mechanisms

10. Technology
Image
Example Resolution Repeatability
Accuracy
per
300mm
Velocity
Control
Ball Screw
Good
(~ 5 µm)
Good
(~ 5 µm)
Good
(~ 15 µm)
Good
(~ 1%)
Lead Screw
Good
(~ 5 µm)
Moderate
(~ 20 µm)
Moderate
(~ 30 µm)
Moderate
(< 2%)
Timing Belt
Low
(~ 50 µm)
Low
(~ 100 µm)
Low
(~ 250 µm)
Low
(< 5%)
Rack &
Pinion
Moderate
(~ 20 µm)
Moderate
(~ 50 µm)
Low
(~ 150 µm)
Moderate
(< 3%)
Linear
Motor
Excellent
(< 1 µm)
Excellent
(~ 1 µm)
Excellent
(~ 5 µm)
Excellent
(<1 %)
Precision

11. Technology
Image
Example Resolution Repeatability
Accuracy
per
300mm
Velocity
Control
Ball Screw
Good
(~ 5 µm)
Good
(~ 5 µm)
Good
(~ 15 µm)
Good
(~ 1%)
Lead Screw
Good
(~ 5 µm)
Moderate
(~ 20 µm)
Moderate
(~ 30 µm)
Moderate
(< 2%)
Timing Belt
Low
(~ 50 µm)
Low
(~ 100 µm)
Low
(~ 250 µm)
Low
(< 5%)
Rack &
Pinion
Moderate
(~ 20 µm)
Moderate
(~ 50 µm)
Low
(~ 150 µm)
Moderate
(< 3%)
Linear
Motor
Excellent
(< 1 µm)
Excellent
(~ 1 µm)
Excellent
(~ 5 µm)
Excellent
(<1 %)
Always needed
Precision

12. Technology
Image
Example Resolution Repeatability
Accuracy
per
300mm
Velocity
Control
Ball Screw
Good
(~ 5 µm)
Good
(~ 5 µm)
Good
(~ 15 µm)
Good
(~ 1%)
Lead Screw
Good
(~ 5 µm)
Moderate
(~ 20 µm)
Moderate
(~ 30 µm)
Moderate
(< 2%)
Timing Belt
Low
(~ 50 µm)
Low
(~ 100 µm)
Low
(~ 250 µm)
Low
(< 5%)
Rack &
Pinion
Moderate
(~ 20 µm)
Moderate
(~ 50 µm)
Low
(~ 150 µm)
Moderate
(< 3%)
Linear
Motor
Excellent
(< 1 µm)
Excellent
(~ 1 µm)
Excellent
(~ 5 µm)
Excellent
(<1 %)
Needed for Scanning Applications
Precision

13. Technology
Image
Example
Mechanical
Efficiency
Wear
Resistance
Dirt
Resistance Maintenance
Ball Screw
Excellent
(80 – 95%)
Good
(Rolling)
Moderate
(Seale)
Moderate
(Lubrication)
Lead Screw
Low
(10 – 50%)
High
(Sliding)
Moderate
(Sliding)
Moderate
(Preload Adj.)
Timing Belt
Excellent
(80-90%)
Excellent
(Tension)
Excellent
(Harsh env.)
Good
(Belt Tension)
Rack &
Pinion
Good
(70-80%)
Moderate
(Pinion)
Moderate
(Jamming)
High
(Lubrication)
Linear Motor
Excellent
(Non-
contact)
Excellent
(Cables)
Poor
(Need
Cover)
Excellent
(None)
Expected Life

14. Technology
Image
Example
Mechanical
Efficiency
Wear
Resistance
Dirt
Resistance Maintenance
Ball Screw
Excellent
(80 – 95%)
Good
(Rolling)
Moderate
(Seale)
Moderate
(Lubrication)
Lead Screw
Low
(10 – 50%)
High
(Sliding)
Moderate
(Sliding)
Moderate
(Preload Adj.)
Timing Belt
Excellent
(80-90%)
Excellent
(Tension)
Excellent
(Harsh env.)
Good
(Belt Tension)
Rack &
Pinion
Good
(70-80%)
Moderate
(Pinion)
Moderate
(Jamming)
High
(Lubrication)
Linear Motor
Excellent
(Non-
contact)
Excellent
(Cables)
Poor
(Need
Cover)
Excellent
(None)
High Efficiency = Long Life
Expected Life

15. Technology
Image
Example
Mechanical
Efficiency
Wear
Resistance
Dirt
Resistance Maintenance
Ball Screw
Excellent
(80 – 95%)
Good
(Rolling)
Moderate
(Seal)
Moderate
(Lubrication)
Lead Screw
Low
(10 – 50%)
High
(Sliding)
Moderate
(Sliding)
Moderate
(Preload Adj.)
Timing Belt
Excellent
(80-90%)
Excellent
(Tension)
Excellent
(Harsh env.)
Good
(Belt Tension)
Rack &
Pinion
Good
(70-80%)
Moderate
(Pinion)
Moderate
(Jamming)
High
(Lubrication)
Linear Motor
Excellent
(Non-
contact)
Excellent
(Cables)
Poor
(Need
Cover)
Excellent
(None)
Environment Control
Expected Life

16. Technology
Image
Example Speed
Accel /
Decel
Frequency
Response Duty Cycle
Ball Screw
Moderate
( < 1.5 m/s)
Good
(~ 3 G)
Good
(30 – 50 Hz)
Excellent
(100%)
Lead Screw
Low
( < 0.5 m/s)
Moderate
(~2 G)
Low
(0 – 30 Hz)
Low
(50%)
Timing Belt
Excellent
( > 10 m/s)
Good
(>3 G)
Low
(20 – 30 Hz)
Excellent
(100%)
Rack &
Pinion
Excellent
( > 10 m/s)
Good
(>3 G)
Low
(20 – 30 Hz)
Excellent
(100%)
Linear
Motor
Excellent
( > 10 m/s)
Excellent
(> 5 G)
Excellent
(50 – 80 Hz)
Excellent
(100%)
Throughput

17. Technology
Image
Example Speed
Accel /
Decel
Frequency
Response Duty Cycle
Ball Screw
Moderate
( < 1.5 m/s)
Good
(~ 3 G)
Good
(30 – 50 Hz)
Excellent
(100%)
Lead Screw
Low
( < 0.5 m/s)
Moderate
(~2 G)
Low
(0 – 30 Hz)
Low
(50%)
Timing Belt
Excellent
( > 10 m/s)
Good
(>3 G)
Low
(20 – 30 Hz)
Excellent
(100%)
Rack &
Pinion
Excellent
( > 10 m/s)
Good
(>3 G)
Low
(20 – 30 Hz)
Excellent
(100%)
Linear
Motor
Excellent
( > 10 m/s)
Excellent
(> 5 G)
Excellent
(50 – 80 Hz)
Excellent
(100%)
Long Moves
Throughput

18. Technology
Image
Example Speed
Accel /
Decel
Frequency
Response Duty Cycle
Ball Screw
Moderate
( < 1.5 m/s)
Good
(~ 3 G)
Good
(30 – 50 Hz)
Excellent
(100%)
Lead Screw
Low
( < 0.5 m/s)
Moderate
(~2 G)
Low
(0 – 30 Hz)
Low
(50%)
Timing Belt
Excellent
( > 10 m/s)
Good
(>3 G)
Low
(20 – 30 Hz)
Excellent
(100%)
Rack &
Pinion
Excellent
( > 10 m/s)
Good
(>3 G)
Low
(20 – 30 Hz)
Excellent
(100%)
Linear
Motor
Excellent
( > 10 m/s)
Excellent
(> 5 G)
Excellent
(50 – 80 Hz)
Excellent
(100%)
Short, Quick Moves
Throughput

19. Technology
Image
Example
Force
Density
Material
Costs
Needs to
Implement
Travel
Length
Ball Screw Excellent Moderate
Motor, Bearings
(linear / rotary)
Moderate
( ~5 feet)
Lead Screw Excellent Good
Motor, Bearings
(linear / rotary)
Low
(~3 feet)
Timing Belt Moderate Excellent
Motor, Bearings
(linear / rotary),
Gearbox
Excellent
( ~30 feet)
Rack &
Pinion
Moderate Moderate
Motor, Bearings
(linear), Cable
Management
Excellent
(> 40 feet)
Linear
Motor
Low High
Bearings (linear),
Feedback, Cable
management
Excellent
(> 40 feet)
Special Considerations

20. Looking at the Pros and Cons ……

21. Precision Ball Screws
When
• High precision applications
with moderate speed (< 1
m/sec).
• Applications requiring very
good repeatability (micron
level)
• Applications requiring high
force densities.
Difficulties
• Requires precision alignment
of screw to path of travel.
• Requires precision angular
contact bearings assembly
design.
• Requires a precision coupling,
which will require precision
alignment of screw to motor
shaft.
• Selecting the right lubricant.
• Can be noisy.
• Maintenance.

22. Lead Screws
When
• For low speed and low duty
cycle applications.
• Non-back driving applications.
• For periodic adjustment
applications
Difficulties
• Low efficiency, requires larger
motors.
• May have resonance issues.
• Requires precision screw
alignment
• .

23. Timing Belt and Pulley
When
• For High speed applications
• When long life maintenance
free operation is important
• Lower precision application
>100um
Difficulties
• Has periodic error due to out-
of-round precision of the
pulleys.
• Has long lead error caused by
pitch diameter precision. (This
can be compensated).
• Must have some form of belt
tensioning.
• Care must be taken in
designing pulley bearing
system to handle loading.

24. Rack and Pinion
When
• Ideal for long travel
applications.
• High speed motion.
• Typically lower precision.
Difficulties
• Alignment of the rail must be
precise, especially in tooth
height.
• Can be noisy, especially spur
type.
• Hard to remove backlash
• Precision is impacted by
tolerance of pinion.

25. Linear Motor
When
• High speed.
• Very high precision.
• No backlash.
• Exceptionally low following
error.
• Fast move and settle times.
• .
Difficulties
• Difficult to use in vertical
applications.
• Magnetic field can be
problematic
• Less Force density compared
to most other drive trains.
• Requires linear feedback for
operation, this drives up over
all cost.
• Can be Expensive.

26. Parker Can Help!!!
Work with Parker and achieve the right
balance:
Precision
LifeThrough-
put

27. Standard Products – not inclusive
Precision Industrial

28. Custom Engineered Solutions

29. High Throughput
Market: Lab Automation
Application: High throughput screening
Solution: Multi-axis belt driven, Cartesian robot

30. Partner with Parker